Method of protecting well casing from damage by strata or other earth slippage



Nov. 25, 3952 J, JACKSON 2,619,323

' METHOD OF PROTECTING WELL pAsING FROM DAMAGE I BY STRATA OR OTHER EARTH SLIPPAGE Filed Jan. '7, 1950 Y SLIPPAGE PLANE $1. PPAGE u PLANE INVENTOR. John Gordon Jackson Qih i4 T/AVJ/QAA ATTORNEYS Patented Nov. 25, 1952 UNITED STATS TNT OFFICE METHOD OF PROTECTKNG WELL CASING FROM DAMAGE BY STRATA OR OTHER EARTH SLIPPAGE Application January 7, 1950, Serial No. 137,316

9 Claims.

This invention relates to the drilling of earth wells and more particularly to a method of well drilling which will prevent damage to well casing when said casing has to be set in a well hole that passes through a plane of slippage between earth strata or any other fault plane where slippage is occurring or may occur.

One of the objects of the invention is to so drill an earth well that when casing is set therein it will not be damaged or severed for a considerable period of time when the casing must intersect a fault plane where slippage is occurring or may occur.

A further object is to so drill an earth hole that a slot will be produced Where said hole must intersect a slippage plane between portions of the earth; and the longitudinal plane of said slot will extend in the same direction as the direction of slippage.

Yet a further object is to so drill an earth hole and set casing therein that damage will not be caused to the casing for a long period of time whenever slippage occurs at a plane between portions of the earth; which plane is intersected by the casing.

A still further object is to so drill an earth hole through a plane of slippage in the earth that the hole from a point above the plane to a point below the plane will be in the form of a slot so positioned with respect to the direction of slippage that when well casing is set to extend through the slot there can be considerable relative movement of the earth portions on opposite sides of the slippage plane without any shearing action on the casing.

A still further object is to provide an improved method of establishing in an earth hole a section of considerable length having the form of a slot.

A further object is to so drill an earth hole that a considerable length thereof beginning at a point below the earths surface will have a different cross section through a major portion of its length with a considerably greater dimension in one direction than in another direction at right angles thereto.

A further and more specific object is to produce a slot section in the length of a well hole by first drilling a bowed-like bore with a drill stem and drill bit and then during the continued drilling of the well hole below the bowed-like bore drilling away earth material at one side of the bore by a reamer bit on the drill stem.

Other objects of my invention will become apparent from the following description taken in connection with the accompanying drawings illustrating the drilling of a well in accordance with steps embodying the invention.

In the drawings:

Figure 1 is a view illustrating the first step in my improved method comprising the drilling of a bowed-like bore through a plane of slippage in the earth and the beginning of the second step of subsequently drilling away earth material at one side of the bore to produce a slot and thereby straighten the hole, the bowed condition of the bore being considerably exaggerated with respect to the length of said bore;

Figure 2 is an enlarged view showing the reamer bit and the drill stem and the manner in which it acts to produce the slotted section as the well is continued to be drilled to a depth below the bowed-like bore;

Figure 3 shows the finished slot section of the hole intersecting the plane of slippage and the casing set therein;

Figure 4 is a cross sectional view of the slot at the plane of slippage; and

Figure 5 is a view illustrating how slippage will not cause damage to the casing because of the slotted section in the well hole where it passes through the plane of slippage.

In the drilling of oil wells and other earth holes it may be necessary to have the well pass through or intersect a plane of slippage between portions of the earth. These planes of slippage may be either faults occurring in a vertical or near vertical direction through the earth and across strata of the earth, or in planes between adjacent strata of the earth. When well holes pass through such planes of slippage and after well casing has been set in the bores, it is readily apparent that as slippage occurs the well casing may be damaged by being pinched or even completely severed by a shearing action. When damage occurs to well casings from slippage between earth portions, the entire well may be lost or so damaged that it is no longer useful and the result will be that it is necessary to drill a new well so that the oil at a point below the plane of slippage may continue to be recovered.

This damage to well casing from slippage between portions of the earth occurs in many different places throughout the world, one particular place being at Terminal Island in the Long Beach area in California. In this particular area the plane of slippage is known and the extent thereof, together with its direction. It has been ascertained that the slippage is at the rate of approximately one foot per year and that the plane of slippage is at approximately sixteen hundred feet below the earths surface. This 3 slippage has resulted in considerable loss to the oil wells which pass through the plane of slippage. Numerous wells have already been lost, due to the oil well casing being severed and the result is that new wells have to be drilled periodically.

In accordance with my invention, I have cliscovered a way in which the well casings can be protected against this damage from slippage for a considerable period of time, notwithstanding that there is a slippage occurring which may be as great as one foot per year. My method for protecting the oil well casing against damage, such as pinching down or complete severing, consists primarily of so drilling the well that when the casing is set in the earth hole drilled there will be present a slot extending between points on opposite sides of the plane of slippage with the plane of the slot extending in the same direction as the direction of slippage movement. By having this slot of considerable depth at the point where it passes through the plane of slippage, the movement of one portion of the earth with respect to the other portion of the earth will then not be able to produce a shearing action or other damaging action on the well casing as there is space provided in proper adjacent relationship to the casing so that movement of the earth can take place without any shearing action on the casing.

Referring to Figure 1 of the drawing, there is disclosed the first step and the beginning of the second step in drilling the well to carry out my method of protecting the well casing against damage from slippage movement. The plane of slippage is generally indicated by the letter P and is at approximately the 1600 foot level beneath the surface, which corresponds to the slippage plane at the above mentioned Terminal Island area. When the well hole being drilled, indicated by the numeral l0, reaches approximately the 1450 foot level, assuming that it is being drilled in approximately a vertical direction, it will then be drilled off at an angle. As shown, the drilling is done by drill pipe H of a rotary drilling apparatus or rig in a well known manner. The drilling of the bore in an angular direction away from the vertical is accomplished by the use of a deflecting tool or whipstock, a known practice in the art of drilling wells by rotary apparatus. The bore it will then have the continued angular section i2 indicated in Figure l. The angle at which the section I2 of the bore is drilled will vary, depending upon how deep a slot is desired to be provided for protecting the well casing. If it should be desired to provide a slot which is approximately 20 feet in depth, then an angle will be selected for the portion of the drill bore [2 that will bring this portion of the bore approximately 20 feet away from the vertical line L when the angular bore [2 reaches the 1600 foot level at which the plane of slippage is occurring. When the plane of slippage is reached, the bore is again caused to take an angular direction so as to bring it back to a point which is vertically below the point in the vertical bore IE3 at which the bore [2 was drilled off at an angle. The result will be an angular bore I3 extending to approximately the 1750 foot level.

It will be seen that the two drilled sectional bores together form a bowed-like bore, which is generally indicated by the letter B, and the greatest distance that this bore has been deflected from the vertical line L is approximately 20 feet and at the plane of slippage P.

In drilling of the bowed-like bore B, comprising the sections l2 and i3, it is necessary that it have a definite position with respect to the vertical line L. This position must be such that a plane which contains both the vertical line L and the bowed-like bore 13 will extend in the same direction as the direction of slippage. In other words, the bore B will be so positioned with respect to the vertical line L that a line drawn between the bore and the line L at the plane of slippage will be in the direction of the slippage movement. The bore B may be on either side of the vertical line L which is toward the mass of earth which is slipping on the mass of earth below it. In other words, if the arrow in Figure 1 indicates the mass of earth M which is moving or slipping on top of the fixed mass of earth F, then the bowed-like bore B will preferably be bowed in the direction indicated, which will be opposite to that of the arrow. After the bowedlike bore B has been drilled, and it is to be noted in Figure 4 that the bowed condition thereof has been excessively exaggerated for the purpose of better illustrating the invention, the well bore is continued to be drilled in its original direction by the drill bit M on the lower end of the drill stem H. However, as the well bore is continued to be drilled, there is placed in the drill pipe II a reamer tool or hit i5 which is best shown in the enlarged View of Figure 2. It is well known that the lower end of the drill pipe just above the drill bit [4 at the bottom thereof is provided with heavy so-called drill collars and it is by means of these drill collars that weight is applied to the drill bit. Because of the weight of these drill collars, it is seen that the bowed portion of the drill pipe where it passes through the bowed-like bore B will be under tension and there will be a tendency to straighten it out, that is, pulled towards the vertical line L as drilling of the well bore continues. Consequently, as the well bore is continued to be drilled by the drill bit l4 and the drill stem moves downwardly, the reamer tool or bit l5 will cut oil? earth material on the inside part of the bore B and thus begin to develop a slot. After the reamer bit [5 has been caused to pass substantially through the bowed-like bore B the drill pipe can be pulled up and the position of the reamer bit properly placed in the drill pipe so that when drilling with the bit I4 is continued, the reamer will be in a position to again drill away more material on that side of the bore B toward the vertical line L. After this passage of the reamer through the bore B has been carried out numerous times, the result will be that all the material, or substantially all the material, which lies between the bore B and the vertical line and indicated by the letter E, will be removed and there will be established a slot S which is best shown in Figures 3 and t. The slot will have a width which will correspond to that drilled by the reamer bit I 5. The slot will extend from the 1450 foot level to the 1750 foot level with its greatest depth, which is shown as 20 feet, being at or near the plane of slippage P. One edge of the slot will be somewhat bowedlike, corresponding to the bowed-like bore 3 and the other edge of the slot will be substantially vertical, depending upon how close the reamer bit can be caused to cut the material E away to a vertical line. During the operation of the drilling by the reamer bit, one or more drift indicators can be employed inside the drill pipe 50 that a close check can be made on how the material is being cut away to form the slot S and the extent to which the slot S grows as it is drilled.

When an oil well is finished, the drill stem of course will be removed and easing set in the drilled well hole. This casing is indicated at C in Figure 3 and where it passes downwardly through the drilled hole and it intersects the plane of slippage it will lie along the substantially vertical edge of the slot S, that is, opposite the bowed-like edge of the slot which was created by the drilling of the bowed-like bore B. The casing at the point just above the slippage plane will thus be approximately 20 feet, or the depth of the slot, away from the earth portion M which is moving relatively to the earth portion F and in the direction indicated by the arrow. Thus, if we consider that the rate of slippage is approximately one foot a year, it will take approximately 20 years for the earth portion M along the curved edge to reach a point where it can engage the well casing and cause any damage thereto, thus the casing will be protected against damage during this time. If the slot were not provided, then there would be no protection to the casing and if there were a movement at the rate of approximately a foot a year, the casing would be sheared ofi after a years time, considering, of course, that the casing is approximately the same diameter as the bore in which it was positioned and both being in the neighborhood or one foot in diameter.

Figure 5 illustrates the condition of the earth portion M and the earth portion F after slippage has occurred ai'er approximately 20 years and at the time that the portion M is beginning to engage the well casing C at the plane of slippage. It will be noted that the whole portion M has moved relatively in the direction of the arrow to the portion F and consequently the casing C above the plane of slippage has been bent, due to the earth acting on the casing at a point above the beginning of the slot S. However, this bending will not cause any damage to the casing as it is only slight, occurring over a distance of approximately 150 feet and amounting only to a distance of 20 feet out of vertical line.

The slot S, although being shown as being on that side of a vertical line toward the oncoming movement of the earth portion M, may be drilled on the opposite side of the vertical line L. However, it is preferred to drill it on the side shown because with such position of the slot, then any earth material which may cave off from the upper angular edge of the slot will fall into the lower portion of the slot and when so caught will have no effect in decreasing the eifect of the slot in protecting the casing since there is no movement of the lower curved edge of the slot in the earth portion F relative to the casing. It is believed to be readily apparent that ii the slot S were drilled on the opposite side of the vertical line than that shown with the same direction of slippage movement involved, then any caving oil of earth material from the upper curved edge of the slot, the lower portion of the slot below the plane of slippage would tend to become filled and as the casing moved with the earth portion M it would tend to be wedged and could not have free movement in all of the lower part of the slot which is in the earth portion F.

It may be desired to prevent any caving over the years at the slot S. This can be done by having the slot S filled with a gelatine-like material G. During drilling of slot S a drilling fluid can be used which, with the addition of a chemical at a certain time, will causethe fluid to thicken. With the thickened fluid in the slot, it will prevent caving, but willnot prevent any relative movement between the casing and the slot. In other words, as there is relative movement between the casing and the slot, due to slippage between the earth portions M and F,

the thickened fluid or gelatine-like material will flow around the casing or it might be said that the casing moves through the gelatine-like material in the same manner as a ball would move through water when it is dropped into a bucket of water. It is also possible to place in the slot suitable gelatine-like material after the casing is set.

Although I have disclosed my methodof so drilling an earth hole that casin will be protected from slippage occurring between two strata of earth, the same method can be used where there are other types of slippage, such as a cross fault, that is, a cleavage of earth strata which cuts across the strata. It is also believed to be apparent that even though the slot is shown as being drilled as a slot to one side of a vertical bore, it can be drilled in relation to any bore other than a vertical bore and the same protection afiorded the casing. However, the slot must extend in the same direction as the direction of the slippage movement and to give maximum protection to the casing, the greatest depths of the slot must be at or near the plane of slippage. Therefore, being aware of the possibility of various ways in which my method and means can be employed to protect casing against damage by earth slippage, I desire it to be understood that the scope of my invention is not to be limited in any manner except in accordance with the appended claims.

What is claimed is:

1. A method of drilling a hole through a plane of slippage between portions of the earth to protect subsequently set casing in the hole from damage from the slippage movement which comprises drilling a, bore by way of an indirect path from a point above the plane of slippage to a point below said plane and then removing earth material at one side of the indirect hole so that there will be established as a part of the hole between said points a slotted section having the plane of its slot aligned with the direction of slippage at a point where it passes through a straight line between the points.

2. A method of drilling a hole through a plane of slippage between portions of the earth to protect a subsequently set casing in hole from damage from the slippage movement which comprises drilling a bore from a point above the plane of slippage to a point below said plane and then so reaming said bore that there will be established in the hole between said points a slotted section having the plane of its slot extending in the direction of slippage.

3. A method of drilling an earth hole to protect subsequently set casing therein which is to extend through a plane of slippage between portions of the earth which comprises drilling from a point above the slippage plane to a point below said plane a bore by way of an indirect path between said points and then drilling away additional earth material laterally from the indirect bore to thereby establish a slot, said drilled bore and the subsequently drilled adjacent earth material being so related with respect to the direction of the slippage that the plane of the slot.

will extend in the same direction as the direction of slippage movement.

4. A method of drilling an earth hole to protect subsequently set casing therein which is to extend through a plane of slippage between portions of the earth which comprises drilling from a point above the slippage plane to a point below said plane a bore by way of an indirect path between said points and then reaming away additional earth material laterally from said indirect bore while drilling additional hole below the indirect bore to thereby establish a slot, said indirect drilled bore and the subsequently reamed adjacent earth material being so related with respect to the direction of the slippage that the plane of the slot will extend in the same direction as the direction of slippage movement.

5. A method of drilling an earth hole to protect subsequently set casing in the hole from damage by movement of one portion of the earth rela- I tively to another portion and in a direction at an angle to the axis of the casing to be set which comprises drilling a bore from a point on one side of the plane of relative movement of the portions of the earth to a point on the other side 01" such plane which will have a bowed-like indirect path between said points with said indirect path lying substantially in a plane containing the direct line between the points and an intersecting line indicating the direction of movement of the said one portion of the earth relatively to the said other portion, and then subsequently removing earth material from the bowed-like bore toward the direct line between the points to produce a slot having a width at least as great as the diameter of the casing to be set and a depth considerably greater than the diameter of said casing.

6. A method of drilling an earth hole to protect subsequently set casing in the hole from damage by movement of one portion of the earth relatively to another portion and in a direction at an angle to the axis of the casing to be set which comprises drilling a bore from a point on one side of the plane of relative movement of the portions of the earth to a point on the other side of such plane which will have a bowed-like indirect path between said points with said indirect path lying substantially in a plane containing the direct line between the points and an intersecting line indicating the direction of movement of the said one portion of the earth relatively to the said other portion, and then subsequently removing earth material from the bowed-like bore toward the direct line between the points during drilling of the hole below the bowed-like bore to thereby produce a slot having a width at least as great as the diameter of the casing to be set and a depth at least several times greater than the diameter of said casing.

'7. A method of drilling an earth hole and setting casing therein so as to protect the casing from being damaged by movement of one portion of the earth relatively to another portion and in a direction at an angle to the axis of the cas ing to be set which comprises drilling a bore from a point on one side of the plane of relative movement of the portions of the earth to a point on the other side of such plane which will have a bowed-like indirect path between said points with said indirect path lying substantially in a plane containing the direct line between the points and an intersecting line indicating the direction of movement of the said one portion of the earth relatively to the said other portion, then subsequently removing earth material from the bowed-like bore toward the direct line between the points to produce a slot having a width at least as great as the diameter of the casing to be set and a depth at least several times greater than the diameter of said casing, setting the casing so as to extend through the slot closely adjacent one edge, and then filling the slot with a gelatine-like substance.

8. A method of drilling by a rotary drilling apparatus an earth hole through a plane of slippage between two portions of the earth so that casing set in the hole will be protected against damage by the slippage which comprises drilling a bowed-like indirect bore between two points on opposite sides of the plane of slippage which bore will be to one side of a direct line between the two points and lying in a plane containing the direct line and an intersecting line indicating the direction of slippage movement, continuing to drill the earth hole below the end of the indirect bore and during said continued drilling cutting a slot in the earth from the indirect bore toward the direct line between the upper and lower points of the indirect bore.

9. A method of drilling by a rotary drilling apparatus an earth hole through a plane of slippage between two portions of the earth so that casing set in the hole will be protected against damage by the slippage which comprises drilling a bore from a point on one side of the plane of slippage at an angle to the direction the hole is being drilled and to the plane of slippage, then drilling the bore in a direction to return to the direction the hole is being drilled, said drilled bore lying in a plane containing the line of direction of the hole and an intersecting line indicating the direction of slippage movement, continuing to drill the earth hole below the end of the said drilled bore and during, said continued drilling reaming a slot in the earth from the bore toward the line of direction of the hole.

JOHN GORDON JACKSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,178,554 Bowie Nov. '7, 1939 2,324,956 Sewell July 20, 1943 

